1. Technical Field
The present invention relates to a semiconductor memory apparatus, and more particularly, to a circuit for controlling a driver of a semiconductor memory apparatus.
2. Related Art
Generally, a semiconductor memory apparatus includes a plurality of drivers with different impedance values so as to correspond to various data input and output impedances, and the plurality of drivers can selectively operated so as to implement various input and output impedances.
Further, a semiconductor memory apparatus has a pre-emphasis function for lowering the impedance at the time of driving transited data, so as to improve the driving capability. Therefore, the semiconductor memory apparatus needs a separate driver to achieve the pre-emphasis function.
A circuit for controlling a driver of a semiconductor memory apparatus according to the related art is described below.
Ask shown in FIG. 1, the circuit for controlling a driver of a semiconductor memory apparatus according to the related art includes first to third drivers 40, 70 and 100; an impedance adjusting unit 10 that outputs a first code PC<0:5> and a second code NC<0:5> for adjusting the impedance value of each of the first to third drivers 40, 70 and 100 to a set value; driver control units 20, 50 and 80, each of which outputs the first code PC<0:5> and the second code NC<0:5> according to a driver enable signal stinf<0:2>; data processing units 30, 60 and 90 that output data (UP: pull-up data, and DN: pull-down data) to the corresponding first to third drivers 40, 70 and 100 according to the first code PC<0:5> and the second code NC<0:5>; an auxiliary driver 120 that reinforces the driving capabilities of the first to third drivers 40, 70 and 100 according to input auxiliary codes; an auxiliary code processing unit 110 that outputs the auxiliary code to the auxiliary driver 120 according to a driving reinforcing enable signal PE; and a pad 130 that is connected in common to output terminals of the first to third drivers 40, 70 and 100 and the auxiliary driver 120 and outputs data to an external device.
Each of the first to third drivers 40, 70 and 100, and the auxiliary driver 120 includes a pull-up driver having a plurality of PMOS transistors and a pull-down driver having a plurality of NMOS transistors. In each of the plurality of PMOS transistors, the source is connected in common to a power supply terminal VDDQ, and the drain is connected to a resistor. In each of the plurality of NMOS transistors, the drain is connected in common to a ground terminal, and the source is connected to a resistor. The number of drivers depends on the circuit design, and FIG. 1 shows an exemplary circuit using three drivers and one auxiliary driver.
The operation of the circuit apparatus for controlling a driver of a semiconductor memory apparatus according to the related art with the above-described structure is herein described.
The impedance adjusting unit 10 outputs a first code PC<0:5> and a second code NC<0:5> for adjusting the impedance of each driver, such that the impedance value of each driver is matched with a prescribed value.
The driver control units 20, 50 and 80 output the first code PC<0:5> and the second code NC<0:5> to the corresponding data processing units 30, 60 and 90, or intercept them according to the driver enable signals stinf<0:2>. For example, when the signal stinf<0> is enabled at a logic high level, the driver control unit 20 outputs the first code PC<0:5> and the second code NC<0:5> to the data processing unit 30, but when the signal stinf<0> is disabled at a logic low level, the driver control unit 20 does not output the first code PC<0:5> and the second code NC<0:5> to the data processing unit 30.
The data processing units 30, 60 and 90 output the pull-up data UP to the first to third drivers 40, 70 and 100 according to the first code PC<0:5>, and output the pull-down data DN to the corresponding first to third drivers 40, 70 and 100 according to the second code NC<0:5>.
Accordingly, the first to third drivers 40, 70, and 100 drive the pull-up data UP and the pull-down data DN.
When a pre-emphasis function needs to be performed according to the data transition, the driving reinforcing enable signal PE becomes enabled and the auxiliary code processing unit 110 outputs the prescribed auxiliary code.
As a result, the auxiliary driver 120 reinforces the driving capability.
That is, the first to third drivers 40, 70 and 100 and the auxiliary driver 120 are connected to each other, and internal resistors thereof are connected in parallel to one another. Therefore, when the auxiliary driver 120 operates, the total impedance value of all of the drivers is reduced, thereby reinforcing the driving capability.
However, the circuit for controlling a driver of a semiconductor memory apparatus according to the related art has the following problems.
First, since capacitance exists in each driver due to a connection node between a transistor and a resistor, as the number of drivers increases, the capacitance increases, which deteriorates the impedance characteristics.
Second, since a separate driver is necessary for the pre-emphasis function, the larger layout area is necessary.